Java EE (Java Enterprise Edition) General Discussion

Hi all. I have been playing around with J2SE for sometime but am new to servlets.
I went through google and many books to start on servlets. They say that I have to get JSDK (servlet development kit) to program servlets.

However, I came across J2EE specs and it says that J2EE comes with all in one bundle and JSDK is not needed. Hence, I assumed that JSDK is not needed any more for programming servlets and considered it the old way. Am I correct?

Do I need the J2EE SDK or JSDK if I want to program servlets?

Its mentioned in the J2EE about "Application Server". I have been wondering what this application server means. Is it the same as Tomcat?. Do I need to install the application server even if I have Tomcat intalled? Can Tomcat be considered as an application server?.

thanks.